Transmissions are devices that transform the speed and torque in vehicles using gears, belts, or other drive components. Most transmission designs use discrete speed ratios: low ratios for acceleration, hill climbing, and heavy hauling, and high ratios for higher-speed travel. They use multiple parallel gear sets between input and output shafts. By changing which gear set carries the loads between the shafts, the speed ratio between the input and output shafts is altered.
Transmissions have also been designed that are continuously variable (CVTs). These generally use friction to transfer load from an input shaft to an output shaft. By altering the radial position of friction rollers, belts, or other components, the speed ratio is changed.
A typical CVT design 10 is shown in FIGS. 1 and 2. It uses a driving (primary) pulley 12, a wide v-belt 14, and a driven (secondary) pulley 16. The speed ratio is adjusted by altering the width of the driving 12 and driven 16 pulleys, so that the v-belt 14 contacts at varying radii on the pulleys 12 and 16. FIG. 1 shows the CVT 10 operating at a lower speed ratio where the driving pulley halves 22 and 24 are separated and the v-belt 14 contacts the pulley halves 22 and 24 at a small radius. The driven pulley halves 18 and 20 are squeezed together by a spring under these conditions, forcing the belt 14 at the output end to contact at a large radius. This configuration offers maximum torque magnification and speed reduction. FIG. 2 shows the CVT operating in a higher speed ratio where the pulley halves 22 and 24 of the driving pulley 12 are positioned close together, forcing the v-belt 14 to contact the pulley halves 22 and 24 at a larger radius and increasing the velocity of the v-belt 14. The increased velocity of the v-belt 14 works against the spring force of the driven pulley 16, forcing the driven pulley halves 18 and 20 apart where the v-belt 14 contacts the driven pulley halves 18 and 20 at a smaller radius. This configuration offer maximum speed magnification.
Most current CVTs rely upon fixed-design mechanical or hydraulic actuation that cannot be easily changed to respond to differing demands, such as varying vehicle cargo loads and operator performance demands. Accordingly, there is need for a CVT actuation system that is more flexible and adaptable than the current state of technology.